Copyright is a form of legal protection provided to the authors of "original works of authorship" including literary, dramatic, musical, artistic, and other intellectual works, including poems, plays, books, movies, musical compositions, photographs, drawings, software, audio recordings, radio and television broadcasts of performances, and choreographed works such as dances.

Copyright is secured automatically when a work is "created"—when it is fixed in a copy or phonorecord for the first time. A phonorecord is the physical object in which works of authorship are contained, including cassette tapes, CDs, LPs, 45 r.p.m. disks, and other formats. The copyright in the work of authorship immediately becomes the property of the author who created the work. Mere ownership of a book, manuscript, painting, or any other copy or phonorecord does not give the possessor the copyright, which belongs to the author.

Copyright protects the form of expression rather than the subject matter, concepts, facts, styles, or techniques within the material. Works consisting entirely of information that is common knowledge and containing no original authorship are not protected by copyright.

Works need not be published to be protected by copyright, nor registered. But copyright owners obtain some advantages to registering a copyright with the Copyright Office of the Library of Congress: Registration establishes a clear public record of the copyright, and is required before a lawsuit seeking to protect work originating in the U.S. may be filed in federal court. If a lawsuit does become necessary, a registered copyright is strong evidence and may enable the copyright holder to recover more damages from an infringer. Registering a copyright also allows for extra protection: a copyright owner can record the registration with the U.S. Customs Service for protection against the importation of infringing copies. Copyright registration may be done anytime within the life of the copyright.

The U.S. Constitution gives an author the exclusive right to his works in Article I, Section 8, Clause 8, also known as the Intellectual Property Clause. This clause also gives Congress the power to enact laws "To promote the progress of science and useful arts, by securing for limited times to authors and inventors the exclusive right to their respective writings and discoveries."

Congress first regulated copyright through the Copyright Act of 1790, and copyright law has evolved since then. The Copyright Act of 1976, though modified since its enactment, controls copyright protection in the U.S today. The 1976 Copyright Act generally gives the owner of copyright the exclusive right to reproduce the copyrighted work, to prepare derivative works, to distribute copies or phonorecords of the copyrighted work, to perform the copyrighted work publicly, or to display the copyrighted work publicly. Copyright law may be found at Title 17 of the United States Code.

Because of changes in the law, copyright remains in effect for different lengths of time, depending whether a work was created, registered, or published after January 1, 1978. A work created on or after January 1, 1978, is automatically protected upon its creation, and endures for the length of the author's life and then for an additional 70 years after the author's death. When two or more authors who did not work for hire create an original work together, the copyright term lasts for 70 years after the last surviving author's death. For works made for hire, and for anonymous and pseudonymous works with no record of author identity, the copyright term will be 95 years from publication or 120 years from creation, whichever is shorter.

Copyright protection for works created before January 1, 1978, is more complex, but generally, those works are protected and the life-plus-70 or 95/120-year terms apply to them as well. Works published before 1923 are in the public domain, and may be used by anyone for any purpose.

Copyrighted material may be used by others who obtain permission from the copyright owner. Additionally, the doctrine of "fair use," which evolved through court decisions and is now codified in Section 107 of the Copyright Act, allows some copyrighted work to be reproduced for certain purposes, such as criticism, comment, news reporting, teaching, scholarship, and research. Section 107 also sets forth guidelines to determine whether use of copyrighted material is in fact fair.

Internationally, there is no copyright that will automatically protect an author's writings throughout the world. Protection against unauthorized use in a particular country depends on the laws of that country, though many countries do have laws protecting foreign works under certain conditions, and international copyright treaties and conventions have simplified the process. The two principal international copyright conventions are the Berne Union for the Protection of Literary and Artistic Property (Berne Convention) and the Universal Copyright Convention (UCC).